1. Field of the Invention
The present invention relates to an optical member inspection apparatus, an image-processing apparatus, an image-processing method, and computer readable medium, for detecting an optical defect such as an abnormality in shape or the like, in an optical member such as a lens or the like.
2. Description of the Related Art
An optical member such as a lens or a prism, etc., is generally designed so that incident light flux is refracted regularly, advanced in parallel, converged onto a point or a line, or diverged. However, if the optical member contains therein a foreign matter such as a cotton waste or the like (so called xe2x80x9cfuzzxe2x80x9d), due to a defective formation thereof, or if the surface of the optical member is scratched when handled by operator after molding thereof, or if foreign matter is affixed to the surface of the optical member, the incident light flux will be scattered, and the desired performance cannot be obtained.
Thus, hitherto, various improvements have been devised for optical member inspection apparatus to detect the defective candidate objects of the optical member, in order to automatically judge whether the optical member is satisfactory or defective. In general, such an optical member inspection apparatus picks up an image of the optical member by a method in which the defective candidate objects may show up on the image data and extracts a region in which defective candidate objects are shown by conducting binary notation processing against the image data obtained by the aforementioned method. In case an area of any one of the regions which show the defective candidate objects exceeds a predetermined threshold value, the optical member inspection apparatus judges that the inspection target optical member is defective.
However, in accordance with the algorithm of the above-mentioned conventional judgement, the information obtained as a result of the inspection merely points out whether the inspection target optical member is satisfactory or defective. For instance for, an optical member which contains only one defective candidate object having an area which exceeds the threshold value, and an optical member which contains many of the defective candidate objects are confronted, it may be said that the degree of defect is greater for the latter than the former. But, the aforementioned conventional algorithm of judgement cannot evaluate the difference of degree of defects between such optical members because of the above-mentioned reason. In addition, if an optical member which contains only one defective candidate object having an area which slightly exceeds the threshold value and an optical member which contains many defective candidate objects having areas which are slightly below the threshold value are compared, the degree of defect of the latter may exceed that of the former. But, based on the above-mentioned conventional control algorithm, the former will always be judged as defective, and the latter will always be judged as satisfactory. Thus, in accordance with the conventional algorithm of judgement, the degree of defects of the inspection target optical members cannot be evaluated. Furthermore, unless the degree of defects of the inspection target optical members is evaluated, even if statistical processing of the inspection results for specified number of the optical members are made, the only thing which can be made clear will be the classification of category of defective candidate objects which exceed respective threshold value.
It is therefore an object of the present invention to provide an optical member inspection apparatus, an image-processing apparatus, an image-processing method, and computer readable media which can numerically express the overall defective or satisfactory degree of the inspection target optical members by putting the position in which each defective candidate object is formed into consideration and by evaluating the influence of each defective candidate object on the whole performance of the inspection target optical member.
An optical member inspection apparatus according to the present invention comprises an image pick-up device which picks up image of an inspection target optical member and which outputs image data indicating the image of the inspection target optical member, an extraction processor which extracts, from the image data, a portion having brightness different from its surrounding in the image data as an extracted object, a graphic feature value measuring processor which measures a graphic feature value of the extracted object, a position measuring processor which measures a position of the extracted object in the image data, a normalization processor which calculates a normalized value of the extracted object by normalizing the graphic feature value measured by the graphic feature value measuring processor by the use of reference in accordance with the position measured by the position measuring processor, and an operation processor which calculates a predetermined evaluation function based on all normalized values calculated by the normalization processor with respect to all extracted object which are extracted from same image data by the extraction processor.
An image-processing apparatus according to the present invention comprises an extraction processor which extracts, from an image data which is obtained by picking up image of an inspection target optical member and which indicates the image of the inspection target optical member, a portion having brightness different from its surrounding in the image data, as an extracted object, a graphic feature value measuring processor which measures a graphic feature value of the extracted object, a position measuring processor which measures a position of the extracted object in the image data, a normalization processor which calculates a normalized value of the extracted object by normalizing the graphic feature value measured by the graphic feature value measuring processor by the use of reference in accordance with the position measured by the position measuring processor, and an operation processor which calculates a predetermined evaluation function based on all normalized values calculated by the normalization processor with respect to all extracted object which are extracted from same image data by the extraction processor.
When constructed in the above-mentioned manner, the graphic feature value of each extracted object extracted from the image data by the extraction processor is normalized by the use of reference according to the position of the extracted object in the image data by the normalization processor. Therefore, if the operation processor executes the evaluation function based on all normalized values calculated with respect to all extracted objects which are extracted from same image data by the extraction processor, a value indicating the degree of overall defects of the inspection target optical member is obtained.
Concretely, the graphic feature value which the graphic feature value measuring processor measures may be area, maximum fillet diameter, average brightness or maximum brightness of the extracted object.
The position measuring processor may measure the distance itself from the position equivalent to the optical axis of the inspection target optical member to the extracted object or discriminate region in which the extracted object is formed among a plurality of concentric regions within the image data.
The normalized processor may calculates the normalized value by executing some kind of function on the measured distance and the graphic feature value in case the position measuring processor measures the distance itself, or may normalize the graphic feature value on the basis of the reference value which beforehand relates to the distinguished region in case the position measuring processor distinguishes a region,. More preferably, the normalization processor may conduct normalization so that the graphic feature value of the extracted object caused by optical defects formed in positions where optical defects greatly influence the performance of the inspection target optical member becomes a comparatively large normalized value, and the graphic feature value of extracted object caused by optical defects formed in positions where optical defects do not influence the performance of the inspection target optical member so much becomes a comparatively small normalized value.
The image-processing method according to the present invention comprises steps of extracting, from an image data which is obtained by picking up image of an inspection target optical member and which indicates the image of the inspection target optical member, a portion having brightness different from its surrounding in the image data as an extracted object, measuring a graphic feature value of the extracted object, measuring a position of the extracted object in the image data, calculating a normalized value of the extracted object by normalizing the graphic feature value by the use of reference in accordance with the position of the extracted object, and calculating an evaluation function based on all normalized values with respect to all extracted object which are extracted from same image data.
A computer readable media according to the present invention stores a program. The program causes a computer to perform method which comprises steps of extracting, from an image data which is obtained by picking up image of an inspection target optical member and which indicates the image of the inspection target optical member, a portion having brightness different from its surrounding in the image data as an extracted object, measuring a graphic feature value of the extracted object, measuring a position of the extracted object in the image data, calculating a normalized value of the extracted object by normalizing the graphic feature value by the use of reference in accordance with the position of the extracted object, and calculating an evaluation function based on all normalized values with respect to all extracted object which are extracted from same image data.